This invention relates to spectrometers, and more particularly, relates to spectrometers employing a spatial light modulator (SLM), such as a deformable mirror device (DMD).
Spectrometers function using the principle of dispersion of light which occurs when rays of light are deviated, typically by a diffraction grating or refracted through a prism. Diffraction gratings behave optically like a multiplicity of very narrow individual slits which cause light rays to be deviated at angles depending upon the wavelength of those rays. Prisms cause dispersion of light since the angle of deviation of a light ray as it passes through a prism is a function of its wavelength; this wavelength dependent angular deviation is due to the fact that optical materials exhibit differing indexes of refraction for differing wavelengths. Spectrometer systems using a prism as a dispersing element have inherent advantages over those using a diffraction grating-type dispersion element since they are more efficient in terms of light transmission and less troubled by any stray light. Accordingly, many existing designs of spectrometers employ prism-type dispersion elements.
In existing spectrometers, light transmitted through a slit is dispersed using a diffraction grating or prism. The dispersed light is then imaged onto a detection focal plane, which typically contains an array of minute photosensitive elements. Most spectrometers include a collimator to make all the light rays incident on the grating or prism parallel. Collimation is necessary to control aberrations which result when non-collimated light is transmitted through the dispersing element. However, current spectrometers are relatively bulky instruments since the optical ray paths tend to be fairly long. In addition, current spectrometers require mechanical motion and rotate the dispersing element to scan wavelengths past the detectors. These mechanical motions cause vibrations and result in wear, which may cause alignment and/or calibration problems.
These and other limitations and disadvantages of the prior art are overcome by the present invention, however, and an SLM spectrometer is provided for measuring the amount of energy associated with various wavelengths in a spectrum.